1. Field of the Invention
The present invention relates to an internal combustion engine, in which a fuel is injected to a preset or predetermined wall of a combustion chamber so that it may be instantly evaporated therefrom and completely burned thereby prevent the emission of hydrocarbons.
2. Description of the Prior Art
Conventionally, a gasoline engine has had a problem that, although the combustion temperature has had to be lowered with a view to eliminating the noxious content in the engine exhaust gases of nitrogen oxides (NOx), an unburned noxious content such as hydrocarbons have been produced to deteriorate the combustion efficiency if the combustion temperature is lowered.
Therefore, a variety of combustion methods and gasoline engines have been studied and developed to enhance the combustion efficiency, without producing an unburned noxious content such as hydrocarbons, under the condition in which the combustion temperature is lowered to restrain the emission of nitrogen oxides (NOx).
It is, however, the present state of the art that this object cannot be sufficiently accomplished because the particles of fuel supplied to the combustion chamber (or cylinder) have large diameters.
A feature of the present invention resides in that the fuel to be burned in the combustion chamber is atomized into fine particles.
In the following experiments, gasoline was used as a typical example of a fuel for an internal combustion engine.
In an internal combustion engine, as illustrated in FIG. 1, if fuel vapors are continuously supplied from an intake passage IP having air (AR) flow therein, through an intake valve IV, into a combustion chamber (or cylinder) CC, the fuel is substantially completely burned in the cylinder.
FIG. 2 illustrates the results of the emissions of the total hydrocarbons THC left unburned (or unburned gasoline), which were measured by normally running a four-cylinder fourcycle gasoline engine having a displacement of about 400 cm.sup.3 per cylinder and a compression ratio of about 8.5 under the fixed conditions of revolutions per minute n=1500 r.p.m., charge of air per second=13.5 g/s and torque=5 Kg.multidot.m while changing the air-fuel ratio A/F of a combustible mixture. As will be understood from FIG. 2, the emissions of the hydrocarbons HC were at low level where the gasoline was in a vapour state, and the results were little changed whether gasoline vapor injection nozzle VN was placed at position A or position B.
As will be understood from FIG. 3, moreover, the combustion efficiency was enhanced to thereby reduce the fuel consumption rate.
If, on the contrary, a small pipe SP is formed with a small hole having a diameter of 0.15 mm, as shown in FIG. 4, to supply a continuous flow of gasoline in a liquid state from the vicinity of the intake valve, the emissions of the hydrocarbons HC are varied in the manner shown in FIG. 5 as the positions and directions of arrangement of the hole are changed in the manners shown at A, B, C, D, E and F.
If fuel is supplied at a right angle to the intake passage IP from the point A which is spaced at some distance from the intake valve IV, the gasoline in the hot intake passage is sufficiently heated into vapors so that the emissions of the hydrocarbons are reduced to such a low level as is equal to that of the case, in which the gasoline is supplied in the vapor state.
Conversely, if the fuel supply is directed straight toward the intake valve IV from the position E, the gasoline is left unvaporized and is supplied to the combustion chamber in the form of liquid flow so that the emissions of the hydrocarbons are increased to high levels.
Moreover, the combustion efficiency .eta..sub.b can reach as high as 97 to 98% in the case of the supply from the point A but falls to 90% in the case of the supply from the point E, as shown in FIG. 6.
As has already been understood from these experimental results, where the gasoline engine is run under stable conditions, it is not always necessary to atomize the gasoline to be supplied to the intake passage into fine particles, which is contrary to the prevailing concept, and the gasoline can be completely burned similarly to the case of the vaporized state, even if it is not atomized in the least but is supplied in the form of a liquid flow to the intake passage upstream of the intake valve.
Upon considering the causes, it has been found that, if the liquid flow into the intake passage is completely gasified into a vapor state immediately before the gasoline is ignited in the combustion chamber (or cylinder) even where the gasoline is supplied in the form of the liquid flow, similar results can be obtained to those of the case in which the gasoline is supplied in the vapor state.
As to the supplying method of the gasoline, in other words, it is necessary to promote not only the gasification of the gasoline in the intake passage but also the gasification of the gasoline sucked into the combustion chamber (or cylinder), and it has been found that the latter is especially important, for preventing the production of an unburned content such as hydrocarbon.
Generally speaking, the gasoline sucked in the engine cylinder is partly atomized into fine particles and partly formed into a liquid film while it is passing through the intake valve.
If the fine particles are brought into a condition under which they are floating in the cylinder, their gasification is effected by the heat transfer between the liquid particles and the surrounding gases so that the gasifying rate is lowered.
If, on the contrary, the gasoline particles are brought into contact with a hot solid surface such as the inner wall of the combustion chamber, the head portion of the piston or the exhaust valve, they are instantly evaporated so that the gasifying rate is remarkably increased.
FIGS. 7(A) and 7(B) illustrate the results of the gasifying rates which were calculated on the basis of studies which have been made by the inventors. FIG. 7(A) plots the time necessary for the gasoline droplets having a diameter of 100 microns to finish their gasification during the intake stroke, whereas FIG. 7(B) plots the time necessary for the gasoline droplets having a diameter of 100 microns to finish their gasification during the compression stroke. In FIG. 7(A), moreover, curve 1 is plotted in the case where the gasoline droplets are floating in hot gases under a pressure of 1 atm, whereas curve 2 is plotted in the case where the gasoline droplets in gases under a pressure of 1 atm are brought into contact with the hot solid surface. In FIG. 7(B), on the other hand, curve 3 is plotted in the case where the gasoline droplets are floating in hot gases under a pressure of 11 atms, whereas curve 4 is plotted in the case where the gasoline droplets in gases under a pressure of 11 atms are brought into contact with the hot solid surface.
In other words, the curves 1 and 3 illustrate the times necessary for the gasoline droplets having the diameter of 100 microns to be gasified while floating in the hot gases.
In the case where the four-cycle engine is turned at 1500 r.p.m., its suction and compression strokes are completed in (60s/1500)/2=20 ms, respectively.
In an actual engine, however, since the average temperature and pressure of the mixture during the suction stroke are 100 to 150.degree. C. and about 1 atm (ata), respectively, a time of 300 to 160 ms is required for complete evaporation so that little gasification takes place during the suction stroke. Since the average temperature and pressure during the compression stroke are increased to 325.degree. C. and about 11 atm (ata), respectively, a time of about 18 ms required for the complete gasification can be almost finished during the compression stroke.
On the other hand, the times required for gasification for the case in which the gasoline droplets having a diameter of 100 microns come into contact with the hot solid surface are illustrated in the curve 2 for the suction stroke and in the curve 4 for the compression stroke. Thus, the gasification can be almost instantly finished if the temperature of the solid surface is raised close to the maximum evaporation rate point a in FIG. 7(A). The point b appearing in FIG. 7(A) is the so-called "Leydenfrost" point. If the solid surface is maintained at the Leydenfrost point, the gasoline droplets do not form a liquid film on the solid surface, when they come into contact, but jump up in a round shape into the hot gases.
The experimental results thus far described are obtained for the gases under stationary conditions. In case the gases are flowing while becoming turbulent, the time necessary for the gasification will be reduced to about from (1/5) to (1/7) of that of FIGS. 7(A) and 7(B).
Even in that case, however, it can be deduced that the time for gasification is far shorter for the case of contacting with a solid surface than for the case of floating in the gases.
Generally speaking, the diameter of the atomized droplets to be sucked into the combustion chamber (or cylinder) is frequently larger than 100 microns. In this case, it is far more advantageous that the droplets are brought into contact with a solid surface.
As the revolutions per minute of the engine are increased, the durations of the suction and compression strokes become shorter than 20 ms so that the aforementioned effects are further improved.